It is known in the art that it is generally not possible to obtain high color fastness when the dyeing of cellulosic fibers with direct dyes is concerned. One utilizes, quite frequently, to improve the fastness of the dyestuff, a number of conventional fixating agents.
The problem is frequently the same when using the reactive dyes and the utilization of the dye and the fixating agent interfere with one another, especially in the case where a soap treatment, following the dyeing is insufficient to eliminate all of the dye that is not fixed. The dye that is not fixed is responsible for insufficient color fastness under humid conditions.
A number of compounds have been proposed to improve the color fastness of the dyestuffs, direct or reactive. Most frequently the products of condensation of formaldehyde with compounds containing at least one amino group, such as the products of condensation of formaldehyde with guanidine, amino-triazine, amino-guanidine, dicyanodiamidine, biguanidine, and especially dicyanodiamide are employed.
Equally recommended, is the addition to the fixating agent, of salts of various metals, with the object of improving color fastness. These metals include salts of copper, chromium or aluminum.
In each case the application of a fixating agent is carried out following dyeing, according to a conventional process carried out by immersion in a bath for a long time, or in a continuous or semicontinuous fashion.
The application of the fixating agent can be carried out during the course of a finishing operation, particularly during the course of treatments carried out by the aid of thermosetting agents added to modify the physical characteristics of the article. In this case, a strengthening of the ability of the fixating agent to improve color fastness is observed.